1. Field of the Invention
The present invention relates to an offroad vehicle. More particularly, the invention relates to an engine for such an offroad vehicle.
2. Description of the Related Art
Offroad vehicles or “ATVs” as they are commonly referred to are designed to be operated over rugged terrain. These vehicles are often operated on steep inclines and declines, on rough roads, and in mud and water.
These vehicles include a frame supported by wheels. In one common arrangement, the vehicle has four wheels. An internal combustion engine is used to power at least one, and commonly all, of the wheels.
In this arrangement, a first drive shaft extends to a front axle and a second drive shaft extends to a rear axle. The first and second drive shafts are driven by a crankshaft of the engine. The vehicle includes a transmission through which the first and second drive shafts are powered by the crankshaft.
It is desirable for the engine and related drive train of the vehicle to have a compact arrangement. In particular, due to the conditions in which these vehicles are operated, a great deal of vehicle stability is desired. This stability is enhanced by providing the vehicle with a low center of gravity and a center of gravity which is near the center of the vehicle, longitudinally and laterally. In this manner, the vehicle is less likely to overturn.
To facilitate this goal, the engine is often arranged so that the crankshaft extends transverse to the vehicle. In this arrangement, the center of gravity of the engine is near the center of the vehicle in both the longitudinal and lateral direction, and the periphery of the engine does not extend far from this center.
On the other hand, this arrangement has the drawback that the rotation of the crankshaft must be transmitted to the first and second drive shafts which are arranged transverse to the crankshaft. The transmission may thus be larger than when the engine is arranged with its crankshaft extending parallel to the drive shafts, thereby increasing the length of the vehicle and offsetting some of the benefits achieved by positioning the engine transverse.